iTunes MacBook Sync....

A friend of mine currently has an iPhone and an iPad.
iTunes is installed on a Windows XP laptop.

If she gets a MacBook and sync's her iDevices will it clear anything on the iDevice??

She is not bothered about anything on the previous laptops and wants to start afresh, but does not want to lose everything on the iDevices.
If connected to a new fresh iTunes library on a MacBook will it simply sync everything from the iDevices across, as we do not want anything lost from the iDevice.......

MacRumors attracts a broad audience
of both consumers and professionals interested in
the latest technologies and products. We also boast an active community focused on
purchasing decisions and technical aspects of the iPhone, iPod, iPad, and Mac platforms.